Well testing projects, completion projects and intervention projects in the offshore environment utilize a subsea test tree which is placed in a blowout preventer stack on the seafloor. This type of landing string permits well flow control while also enabling rapid disconnect of the wellhead from a dynamically positioned or anchored vessel. Valves in the subsea test tree are actuated using electrical signals from the vessel to operate solenoids which control flow of hydraulic fluid for positioning the valves. The hydraulic pressure and electrical signals for controlling the system are supplied from the vessel using an umbilical which extends down to the subsea test tree.